Zone purification device



Jan. 20, 1959 E. R. CAPlTA 2,870,309

ZONE PURIFICATION DEVICE Filed June 11, 1957 2 Sheets-Sheet 1 "1 4|1||ill! ll INVENTOR.

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M MNI Jan. 20, 1959 E. R. CAPITA 2,870,309

ZONE PURIFICATION DEVICE Filed June 11, 1957 2 Sheets-Sheet 2 nnuhuuuuuhuu'uuun INVENTOR. 5W1. CAP/ P1 ATTOQA E/ United States Patent ZGNEPURIFICATION DEVICE Emil R. Capita, North Bergen, N. J.

Application June 31, 1957, Serial No. 665,094

12 Claims. (Cl. 219-10.43)

Thepresent invention relates to induction heating in a high vacuum or aninert atmosphere and more particularly to a device for inductivelymelting a short zone of an elongated specimen and for moving the meltedzone along the specimen.

The melting of a short zone of an elongated specimen in a vacuum or inan inert atmosphere is used in known processes of zone purification forsemiconductor or metallic materials such as germanium, silicon, iron,etc. In the zone purification of such rods a short zone of the rod ismelted and the molten zone is then moved longitudinally of the rod. Themoving molten zone acts as a distributor of impurities in the rods to ahigh degree or to increase or decrease the impurity or soluteconcentration in predetermined portions of the rods as required. Inorder to provide for a high degree of purity or to permit apredetermined distribution of the impurities, it is necessary to carryout the zone purification in high vacuums or inert atmospheres and toprovide for movement of the molten zone along the rods with a minimumamount of vibration or movement of the specimen rods themselves. Zonepurifiers now in use do not provide the necessary combination of aneutral atmosphere and a smoothly operating zone motion. The apparatusof the present invention is an improvement upon known types of zonemelting devices which provides for an improved control of the zonemotion while the specimen rod is mounted in a high vacuum or an inertatmosphere. A novel device is provided which moves the molten zonesalong the rods while the rods themselves are mounted with freedom fromvibration and longitudinal motion.

Accordingly, an object of the present invention is to provide animproved means for zone purification.

Another object of the present invention is to provide a zonepurification device which provides for vibrationfree mounting of thespecimen.

Another object of the present invention is to provide an improvedinduction type zone purifying device.

Another object of the present invention is to provide an improvedinduction type zone purifying device having movable induction heatingcoils.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiment about to be described, orwill be indicated in the appended claims, and various advantages notreferred to herein will occur to one skilled in the art upon employmentof the invention in practice.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawings,forming a part of the specification, wherein;

'Fig. 1 is a side elevational view partially in section of the zonepurification device of the present invention;

Fig. 2 is a sectional view taken along the line 2-2 of I Fig. 1;

Fig. 3 is an enlarged fragmentary sectional view of the inductionheating coils;

Fig. 4 is a sectional view taken along line 4-4 of Fig. 3; and

Fig. 5 is a schematic diagram of the coils.

The rodlike specimen 1 of germanium or silicon or other material ismounted between holders 2 and 3 on support rods 4 within a transparentairtight cover or jar 5. The jar 5 is mounted by an airtight sealindicated at 6 on a platfor1n7 which is supported on a stand indicatedgenerally at 8.

In order that the specimen 1 may be positioned vertically during thezone purifying operation, the platform 7 is attached to the stand 8 byadjustable gimbals 9 and 10. As seen in Fig. 2, the gimbal 9 ispivotally mounted by its shaft 11 in bearings 12 on the top 14 of thestand 8 and the position of gimbal 9 is adjusted by threaded adjustorscrew 15 which engages the stand top 14 to position the arm 16 on gimbalshaft 11 against the force of compressed spring 17. The gimbal 10 isrotatably mounted in gimbal 9 on shafts 19 and 20 and its position isadjusted by the rotation of threaded adjustor screw 21 which engages thearm 22 fixedly mounted on the outer end of gimbal shaft 19 and whichmoves the arm against the force of the compressed spring 24. Levelguages 25 (Fig. 2) are mounted on the gimbals to assist in theiradjustment so that the platform 7 which is attached to inner gimbal 10by brackets 26 may be adjusted to a horizontal position.

In order to provide an atmosphere within the jar 5 which is inert withrespect to the specimen 1, a vacuum system 30 is connected to theinterior of the jar 5 through an outlet tube 31. In the preferredembodiment the vacuunrsystem 30 comprises a dilfusion pump 32 with aback-up pump (not shown) connected thereto through valve 35 in theconventional manner. The vacuum apparatus connected to the outlet tube31 comprises a conventional high-vacuum pumping arrangement and afurther description is therefore unnecessary. The vacuum system 30 isthe preferred means for providing a pure atmosphere about the specimen1; however, with certain specimens and where inert gases of extremelyhigh purity are obtainable, the vacuum system 30 may be replaced by aconnection to a source of inert gas.

The induction heating means used to melt a short longitudinal zone ofthe specimen 1 comprise a primary coil 36 positioned outside the jar Sand a secondary coil 3'7 energized thereby and positioned within the jar5 adjacent to the specimen 1. A mounting system 38 is provided for thecoils 36 and 37 which moves the coils longitudinally of the specimen 1in synchronism with each other and which also is adapted to moveauxiliary induction coils in synchronism with the heating coils 36 and37. As illustrated in Figs. 3-5, the secondary heating coil 37 comprisesa single turn having an inner portion 37a closely spaced from thespecimen 1 to provide for efiicient heating of the specimen 1 so thatthe zone 1a may be melted by the currents induced therein by the heatingcoil 37 without auxiliary heating elements.

In the embodiment illustrated, additional coils are illustrated in theform of molten zone supporting coils 39 and 40. Coil 39 is a primarycoil mounted outside the jar S and coil 40 is a secondary coil energizedby the primary coil 39 and mounted within jar 5. The secondary coil 40is mounted below the molten zone 1a and it induces currents thereinwhich are repulsed by the currents in coil 40 so that the repulsionbetween the two currents tends to support the molten zone In against itsnatural tendency to flow downwardly on specimen 1. Coil 40 is shown withtwo turns each having a portion 40a bending inwardly adjacent to thespecimen 1. As will now be more fully described, the mounting system 38supports the four coils 36, 37, 39, and 40 in a fixed relaantennationship with respect to each other and movable with respect to thespecimen 1.

The mounting system 33 is fixedly connected to the platform 7 inperpendicular relationship therewith by its support arm 41, which isattached to the outer end Ztla of gimbal shaft 28. The support 41 willtherefore be adjusted to a perpendicular position when the platform '7is adjusted to a horizontal position by adjustor screws and 21. Coilsupport rod 42 is slidably mounted in bearing brackets 43 on the supportarm 41. The primary heater coil 36 and the primary auxiliary coil 39 aremounted on bracket 44 which is adjustably positioned on the support rod42 by clamping screw 4-5. Coils 36 and 39 are attached to and supportedby suitable terminals 46 and 47 which are adapted for connection tosuitable oscillators (not shown). The secondary coils 37 and 4-0 arealso mounted on the support rod 42 through the intermediation of bracket48 and support rods 49 and 50, respectively. The bracket 48 isadjustably positioned on the support rod 4-2 by the clamping screw 51.The support rods 49 and 5t) slide in airtight bearings 52 and 54 in theplatform 7 so that they are enabled to reciprocate vertically withrespect to the specimen 1. A threaded connection is provided between thesupport rods 49 and 56 and the arms 55 and 56 of the bracket 48 to allowfor fine adjustments of the positions of secondary coils 37 and withrespect to each other and with respect to the primary coils 36 and 39.The threaded connection comprises nuts 57 and 53 which engage thethreaded portions 59 and 66 of support rods 49 and and which arerotatably positioned in slots a and 56a of the bracket arms 55 and 56.

As each of the coils 36, 37, 39, and 40 is connected to the support rod42, the coils will move in synchronism as the rod 42 moves in itsbearing brackets 43. In the preferred embodiment, the support rod 42 hasa hydraulic cylinder 61 at its lower end which is adapted to move thesupport rod 42 up and down as is required for the particular purifyingoperation being used. A piston 62 is connected to the support rod 42 andthe admission of hydraulic fluid under pressure to either inlet 63 or 64moves the support rod 42 and the attached coils up .or down with respectto the specimen 1.

The secondary coils 37 and 40 are preferably hollow and are watercooled. The cooling system for coil 37 comprises a supply tube 65adapted for connection to a suitable water or other coolant source and adrain tube 66. The tubes 65 and 66 pass through the hollow center of thesupport rod 49. The tubes 65 and 66 have at least their bottom portionsformed of rigid metal to support the secondary coil 37 and they areconnected in the electrical center of the hollow secondary coil 37 toprovide a ground potential at this point. As seen in Fig. 4, a baffle 67is provided between the connection of tube 65 and tube 66 so that thecoolant passes completely around the coil 37 in the direction of thearrows as it flows from the supply tube 65 to the drain tube 66. Thesecondary coil 40 is also mounted on and cooled by a water supply tube68 and a drain tube 69. These tubes are connected at opposite sides of abaffie 76) (Fig. 3) which requires the coolant to flow completely aroundthe secondary in passing from the supply tube 68 to the claim tube 69.Tubes 68 and 69 are connected to the electrical center of the secondary40 to ground this point.

A drive system adapted to rotate the specimen 1 or its longitudinal axisto equalize the melting effects is indicated generally at 71. The drivesystem 71 comprises a drive motor 72 with a suitable speed reducer '73which drives the vertical drive shaft '74. A magnetic coupling member 75is mounted on the upper end of the drive shaft 74 which comprises ahousing 76 rotatably mounted on bearings 77 which engage the fixed shaft78 on the bottom of the outlet tube 31. Permanent magnets 79 on thehousing 76 are magnetically coupled to permanent magnets 86 on the gearshaft 81 which is rotatably mounted within the outlet tube 31 and whichis coupled to the lower specimen holder 3 by step-down gearing indicatedat 82. In order to avoid the transmission of any vibration from the geartrain 82 to the specimen 1, the coupling between the specimen 1. and thelast gear train 82 is a flexible coupling 84 with spring members 85.

The upper specimen support 2 is rotatably mounted on the support bracket87 by a bearing indicated at 88. A locking screw 89 is provided toprevent the rotation of the upper end of specimen 1 when it is desiredto rotate only the lower portion to stir the molten zone la. A splashpan 36 is mounted beneath the specimen 1 to protect the gear train frommetal splashes.

The operation of the above-described zone purification device will nowbe described.

The platform 7 is first adjusted to a horizontal position by theoperation of the adjusting screws 15 and 21 on the gimbals 9 and 1t).Specimen i is then mounted on the holders 2 and 3 and the airtight cover5 is placed in position on platform 7 over the support rods 4. Theatmosphere within the airtight cover 5 is now purified by the creationof a vacuum therein by the operation of the diffusion pump 32 and thebacking pump. These pumps draw the air out of the airtight cover 5through the outlet tube 31 to form a substantially complete vacuumwithin the airtight cover 5 and surrounding the specimen 1. Thehydraulic cylinder 6 is now used to move the coil support rod 42 and theattached coils 36, 37, 39, and 4-0 to their desired starting positionwith relation to the specimen 1. This position will depend upon theparticular purification process being used with the particular specimen1 mounted in the zone purifying device. When the coils have been movedto the starting position, the oscillators which are connected to theprimary coils 36 and 39 through terminals 46 and 47, respectively, areenergized. The specimen heating currents are now induced in thesecondary 37 and in the specimen 1. A short longitudinal zone lla (Fig.3) of the specimen 1 is now melted by the current induced in thespecimen 1 from the secondary 37 of the heating coils. A repulsivesupporting force is provided for the molten zone 1a by the currentsinduced therein by the auxiliary secondary coil 4-0 which is positionedbeneath the melting coil 37 and the molten zone In.

Once the molten zone 1a has been formed on the specimen 1, the zonepurification process requires the molten zone In to be movedlongitudinally along the specimen 1. This is done by admitting hydraulicfluid through the hydraulic cylinder inlets 63 or 64 to move the coilsupport rod 42 upwardly or downwardly, respectively, as is necessary forthe particular purification operation being performed and at a speedwhich is controlled by controlling the rate of flow of the hydraulicfluid into the hydraulic cylinder 6t). Since the primary coils 36 and 39are rigidly attached to the support rod 42 on bracket 44 and since thesecondary coils 37 and 40 are also rigidly connected to the support rod42 by means of the bracket 43, the coils will maintain a constantrelationship with respect to each other as they are moved along thespecimen ll. During the motion of the coils, the airtight cover 5, whichis preferably a glass jar, acts as an insulator between the primary andthe secondary coils. In order to equalize the heating effect of coil 37around the circumference of the specimen 1, specimen 1 is rotated bydrive motor 72. Preferably the drive motor 72 is a variable speed motorso that the rate of rotation of the specimen 1 may be adjusted.

During the purifying operation, the overheating of the secondary coils37 and 40 is prevented by the admission of coolant to the coils throughthe inlet tubes 65 and 68. respectively.

When the zone purification has been completed by the movement of themolten zone 1a along the specimen 1 to the extent required, drive motor72 and coils 36 and operation is simplified.

39 are de-energized along with the diffusion pump 32 and the backingpump. The air pressure is then raised within the cover 5 to cotter-{30ndto the outside pressure and the cover 5 is removed to permit the removalof the specimen 1.

It will be seen that the present invention provides an improved zonepurification device which provides for the zone purification of arodlike specimen in a pure atmosphere with a minimum amount of vibrationand with no longitudinal motion of the specimen. The zone purifyingdevice permits the use of heating coils as well as auxiliary coils andprovides for the synchronized movement of all the coils so that they allmay be operated with corresponding motions. The heating coil is adaptedto initiate the zone heating without auxiliary heating means so that thestarting of the zone purifying Cooling means are provided for thesecondary coils adjacent to the specimen to permit theirefiicient-operation with high induced currents Without overheating. Thezone purifying device of the present invention is also adapted forautomatic operation so that the melted zone on the specimen may be movedlongitudinally of the specimen in the desired pattern and so that thespecimen may be simultaneously rotated on its longitudinal axis with aminimum of supervision.

As various changes may be made in the form, construction and arrangementof the parts herein without departing from the spirit and scope of theinvention and without sacrificing any of its advantages, it is to beunderstood that all matter herein is to be interpreted as illustrativeand not in a limiting sense.

Having thus described my invention, I claim:

1. A zone purification device for refining an elongated solid metallicbody comprising the combination of an airtight enclosure adapted tocontain an elongated specimen of the solid metallic body, a transformerincluding a primary coil outside said airtight enclosure and a secondaryheating coil within said airtight enclosure adapted to encircle closelya portion of the specimen, and said primary coil and saidsecondary coilconnected to a common movable support means whereby the secondary coilmay be moved along the specimen while maintaining a fixed positionrelative to said primary coil.

2. A zone purification device comprising the combination of an airtightenclosure adapted to contain an elongated specimen, a transformerincluding a primary coil outside said airtight enclosure and a secondaryheating coil within said airtight enclosure adapted to encircle aportion of the specimen, said primary coil and said secondary coilconnected to a common movable support means whereby the secondary coilmay be moved along the specimen while maintaining a fixed positionrelative to said primary, a second transformer having a primary coiloutside said airtight enclosure and a secondary coil within saidairtight enclosure adapted to encircle the specimen at a position spacedfrom said firstmentioned primary coil, and said primary coil and saidsecondary coil of said second transformer being mounted on said movablesupport whereby they move in a fixed relationship to each other and tothe primary coil and the secondary coil of said first transformer.

3. A zone purification device comprising the combi nation of an airtightenclosure adapted to contain an elongated specimen, a transformerincluding a primary coil outside said airtight enclosure and a secondaryheating coil within said airtight enclosure adapted to encircle aportion of the specimen, said primary coil and said secondary coilconnected to a common movable support means whereby the secondary coilmay be moved along the specimen while maintaining a fixed positionrelative to said primary and said secondary coil being hollow and beingadapted for connection to a source of coolant.

4. The zone purification device as claimed in claim 1 in which saidairtight enclosure is coupled to an air evacuating means.

5. The zone purification device as claimed in claim 2 in which saidsecondary coils are each hollow and are each adapted for connection to asource of coolant.

6. A zone purification device comprising the combination of an airtightenclosure, an outlet on said enclosure, spaced holders mounted withinsaid enclosure and adapted to support an elongated specimentherebetween, one of said holders being rotatably mounted, a drive meansoperatively coupled to said one holder, and heating means for saidspecimen comprising a primary coil outside said enclosure and asecondary coil within said enclosure and adapted to encircle a portionof a specimen mounted in said holders.

7. The device as claimed in claim 6 in which said drive means comprisesa drive motor positioned outside said enclosure which is coupled to saidone holder through a wall of said enclosure by an airtight coupling.

8. The device as claimed in claim 7 in which said airtight couplingcomprises a magnetic coupling.

9. A zone purification device comprising the combination of an airtightenclosure, a pair of spaced specimen holders in said enclosure adaptedto mount an elongated specimen therebetween, an outlet on saidenclosure, an adjustable support for said enclosure movably mountedwhereby said specimen may be positioned vertically, a transformerincluding a primary coil outside said enclosure and a secondary heatingcoil within said enclosure adapted to encircle the specimen, a commonsupport means for said coils attached to said enclosure support andmovable therewith, and said coils connected to said support meansthrough the intermediation of a reciprocable member mounted for motionparallel to the specimen whereby the secondary coil is movable along thespecimen with the primary coil maintained in fixed relationship to thesecondary coil.

10. The device as claimed in claim 9 in which said enclosure supportcomprises a pair of gimbals rotatably References Cited in the file ofthis patent UNITED STATES PATENTS 2,555,450 Lee June 5, 1951 2,743,199Hull et al. Apr. 24, 1956 2,792,317 Davis May 14, 1957

